A coupling device disclosed in the European patent publication EP 1038138 B1 of this type comprises a sleeve-like collet with a meandering shape having gripping teeth distributed on two axially spaced clamping areas. The gripping teeth are arranged on axially extending support arms of the clamping sleeve and function as actuating portions able to be respectively acted on by an actuating face arranged on the inner periphery an actuating sleeve encircling the collet, when the actuating sleeve is shifted axially out of a non-actuated position. The actuating faces are in this case portions of an annular face formed on the inner periphery of the actuating sleeve. Since in the case of this coupling device a relatively large number of gripping teeth must be operated, a relatively large actuating force at the actuating sleeve is required.
A similar situation exits in the case of coupling device disclosed in the German patent publication 10058967 A1, which differs from the above described one essentially in that the collet is made up of two collet elements able to be inserted into each other.
In the case of coupling device described in the European patent publication EP 0811801 A1 there is a thrust ring slotted from either end which is clamped between a main body and a actuating sleeve. On operation of the actuating sleeve the gripping teeth formed by the end portions are simultaneously bent inward radially and braced against the inserted fluid line. In this case as well the actuating force necessary for the actuating sleeve is relatively large so that for its actuation it is best to employ a tool.
In the case of the plug-in fitting described in the German patent publication DE 40 02 057 A1 an axially moving collet is employed having a plurality of axially extending support arms on which respectively one head portion is mounted in a pivoting manner, said head portion having two axially spaced gripping teeth. On shifting the collet a stationary actuating sleeve is thrust against the head portions so that the gripping teeth arranged thereon are simultaneously thrust radially inward. In order to ensure that the gripping teeth may take a proper hold on the fluid line, in this case the collet must be shifted applying a relative heavy force and this makes handling inconvenient.
The German patent publication DE 10 2005 017 692 B3 finally discloses a coupling device in the case of which several components resiliently of a cage element are used. The required holding force in this case comes from the build up of return force, when the gripping teeth are spread apart by the inserted fluid line. For release of the connection the gripping teeth are able to be acted on by means of an axially sliding release sleeve so that they come clear of the outer periphery of the fluid line. In the course of this release operation all gripping teeth simultaneously lift clear of the fluid line. A disadvantage of this coupling device is inter alia also that owing to lack of any active actuation of the gripping teeth it is not always possible to ensure a proper engagement with the inserted select, if its outer dimensions are subject to substantial manufacturing errors. In this case a coupling device is substantially more secure as regards its functions, if it has a actuating sleeve acting actively on a collet, there furthermore then being no relaxation problems as regards the gripping teeth which are normally elastically attached.